A variety of food products containing meat are readily adaptable to replacement of their normal meat constituents with textured vegetable protein. These foods include low-acid tomato-based sauces such as spaghetti sauce, taco, chili mixes, etc. Many of these are low-acid foods and can be stabilized to prevent spoilage due to growth of microorganisms. Purely thermal sterilization leads to loss in flavor acceptability due to the development in the product of burned and browned flavors, as well as thermal reaction product off flavors.
By acidification of such products to a pH of 4.6 or below, the products are rendered microbiologically safe if the products are sealed into containers at elevated temperatures, and held for sufficient time to destroy molds, yeasts, and vegetative bacteria prior to cooling. Safety concerns aside, most acidified foods are kept at a pH well below 4.6, because above about 4.2, growth of Bacillus coagulans occurs, causing flat sour spoilage of the product.
The federal regulations (Food and Drug Administration) permit canners of low-acid foods to acidify their products to a pH of 4.6 or below to prevent the occurrence of botulism.
Rice et al, in a journal paper from the New York State Agricultural Experiment Station (1953), state that increases in citrate level produced proportionate increases in the minimum pH at which strains of Bacillus coagulans are able to germinate and grow. Ashton et al., in Abstracts of the Annual Meeting--1977 of the American Society for Microbiology, state that titratable acidity proved to be a highly reliable index of microbial stability in hot-fill acid foods. Products with titratable acidities greater than 0.5% as acetic acid conferred shelf stability.
Sognefest et al, Food Technology, 1(1), 78 (1947), describe a method of canning tomato juice and tomato juice cocktail at a pH below 4.5 which employs high-temperature short-time processing in a heat exchanger prior to filling in cans.
When meat analog is added to low acid food, e.g. spaghetti sauce, the analog acts as a buffer and raises the pH of the sauce. The high protein and fat content as well as the available water provides a fertile growth medium for bacteria. This also holds true for low acid sauces containing meat or poultry.
It has now been discovered that at a pH of about 4.4, or lower, textured vegetable protein present in low acid food products acquires a sharp, sour, astringent flavor, presumably due to some chemical change in the material at this pH. Clearly, it is desirable to have a process for sterilization of low-acid food products containing significant amounts of textured vegetable protein (meat analog) which rigorously protects product safety, while having minimal impact on product flavor.
It has also been discovered that the presence of meat analog in low acid food products has the unexpected effect of causing increased susceptibility to flat sour spoilage by Bacillus coagulans at pH levels that are usually safe from spoilage. For example, spaghetti sauce without meat analog at pH 4.2 did not spoil after inoculation with B. coagulans spores, while sauce containing analog showed spoilage. Hence, it is also desirable to provide a process for sterilization of low-acid food products containing meat analog which solves this unexpected spoilage problem caused by the presence of analog.
It is an object of this invention therefore to provide a process which renders a food product containing high levels of textured vegetable protein bacteriologically safe and shelf-stable and which operates in a zone of pH (4.2 to 4.6).
It is a further object of this invention to provide a process for sterilizing low acid foods containing at least 7% meat or poultry.
This and other objects will become obvious from reading the disclosure provided herein.
All percentages are by weight unless otherwise indicated.